1. Field
The present invention relates to a method and apparatus for performing activation/deactivation of a secondary serving cell when a user equipment is connected to two different base stations supporting a dual connectivity in a wireless communication system.
2. Discussion of the Background
In a wireless communication system, a user equipment (UE) may perform a wireless communication through two or more base stations among a plurality of base stations each configuring at least one serving cell. This feature may be referred to as dual connectivity. In other words, the dual connectivity may be an operation in which a UE that is configured in a Radio Resource Control (RRC) connected state with at least two different network points uses radio resources provided by the at least two network points. Here, the at least two network points may be a plurality of base stations, which are physically or logically distinguished from each other, and one of the at least two network points may be a master base station (MeNB: Master evolved NodeB) and the others of the at least two network points may be one or more secondary base stations (SeNB: Secondary evolved NodeB).
In dual connectivity, a base station transmits downlink data and receives uplink data through a bearer configured for a UE. Here, a bearer may be configured through one base station or may be configured through the at least two different base stations. Further, in dual connectivity, at least one serving cell may be configured for each base station, and each serving cell may be operated in an activation or deactivation state. A primary serving cell (PCell), which is configurable according to existing carrier aggregation (CA) scheme, may be configured in the master base station. In the secondary base station(s), only secondary serving cell(s) (SCell(s)) may be configured. The CA scheme is a technology to effectively use divided narrow bands, and the CA scheme may provide an effect that a base station uses a logically wide band by aggregating physically continuous or non-continuous bands in a frequency domain.
When a UE is connected to a base station, the base station transmits to the UE an activation/deactivation indicators for secondary serving cells configured for the base station to optimize the battery consumption of the UE, and the UE activates or deactivates secondary serving cells configured for the UE based on the indicator received from the base station. However, in dual connectivity, if the master base station and secondary base station each transmits activation/deactivation indicators for a whole secondary serving cells configured for the respective base station, a problem that a base station also indicates activation/deactivation of other serving cells provided by other base stations may be occurred since the activation/deactivation indicators transmitted from each of the base stations may include activation/deactivation indicators for all secondary serving cells configured for the UE. Moreover, in dual connectivity, each base station has a Medium Access Control (MAC) scheduler, respectively, and each MAC scheduler is operated independently. Accordingly, it is not possible to determine activation/deactivation for serving cells configured of other base station. Thus, there is a need to resolve above the mentioned problems.